Golf is a game that is played and enjoyed by individuals of all ages. Over the years, golf equipment has improved with the advent of improved materials and techniques. Advancements have been made in the design of golf clubs and the materials utilized in their construction. Golf clubs are designated as “woods” and “irons.” Irons include clubs numbered 1 through the wedges. “Woods” is a term applied to drivers, two woods, three woods and so on, which may be fabricated from wood or, more recently, from more exotic materials such as titanium. The trend has been toward utilization of more sophisticated materials in the construction of golf club shafts such as graphite and use of materials such as titanium in the fabrication of golf club heads. The reason for these changes is to provide equipment which will enhance the performance of golfers. The wood clubs typically have longer shafts ranging from 43″ to 47″ in length whereas the irons have shorter shafts. Irons decrease in shaft length as the number of the iron increases. For example, a one iron will less loft and have a much longer shaft than a pitching wedge.
One approach to providing improved performance is to design clubs that provide the golfer consistent feel regardless of a particular club that is selected. The term “feel” is a highly subjective term, but certain physical characteristics of the club can be designed into a set of clubs to attempt to achieve uniformity of feel. Various characteristics which are selected include swing weight, flex and shaft stiffness. “Flex” is the common term given to the bending properties of a golf club. Flex is often identified by a letter, as for example “L” standing for ladies clubs, “A” for amateur, “R” for regular, “S” for stiff and “X” for extra stiff. The flex point of a shaft is the point of maximum bend when the shaft is bent. Shafts with a high kick point may feel more rigid than shafts with low kick points. Swing weight relates to the weight of the shaft. Swing weight measurement relates to overall weight of the club during the swing and 3 grams equals approximately one swing weight point.
When discussing shaft, “torque” refers to ability of shaft resist twisting force about its center line. A high torque rating means the club is low in resisting twist and is high in torsional twist or deflection. One particular characteristic is vibration frequency of the golf club shaft. Vibration frequency is typically defined as the oscillation of the shaft in cycles per minute (cpm) of shaft when it is secured at its butt end in a vice or clamp with the opposite end being free. The free end of the shaft is then manually deflected and released and the oscillation measured.
Many golfers have found a greater consistency in feel and control within a set of clubs is obtained when the vibration frequency are within a certain range.
U.S. Pat. No. 4,070,022 relates to a method of producing matched golf clubs which comprises the steps of determining under similar conditions the frequency of each golf club shaft of a plurality of shafts. Shafts are selected from the plurality such that the frequencies fall on a predetermined gradient line formed by a plot of shaft frequency of shaft length. Frequency increments between successive shaft lengths along a gradient line are substantially equal. The gradients are substantially straight line and increases as shaft length decreases and the frequency increments between successive shaft lengths along the gradient are substantially equal. This approach is representative of a number of golf club manufacturers and sometimes termed “flat line frequency” matching.
Other approaches to the production of a matched set of golf clubs can be found in U.S. Pat. No. 5,040,279. In this method, an electronic frequency analyzer measures the vibrational frequency of the shafts or clubs. Basically this patent deals with the problem of obtaining accurate frequency measurement for composite shafts which have non-uniform cross sections. The patentee suggests there exists certain chordal planes which will yield more consistent frequency measurements if the shaft is caused to oscillate in such plane.
U.S. Pat. No. 5,722,899 discloses methods of making a set of golf clubs that are matched according to vibration frequency. The method includes a random selection of shafts from a stock of raw shafts wherein the vibration frequency of each shaft is determined and then each shaft assigned a club head number. Conversion values are based on the desired actual club head weight for each shaft and by determining a value between a desired and measured frequency of each shaft, a total frequency conversion value may be obtained. The total frequency conversion value may then be used to determine an amount to trim each shaft and thereby linearly match each shaft to the set based on vibration frequency and an increase in club head number.
Thus, from the foregoing, it will be seen that the prior art suggest various golf club manufacturing techniques in which vibration frequency is used as a parameter in matching golf clubs. However, the prior art generally suggests that frequency be linearly matched so that as the club head number increases, the stiffness will decrease in a generally linear relationship. The result is that each club will have a different feel to the golfer.